1. Field of the Invention
The present invention relates to gain control of a power amplifier, and more particularly, to an audio processing chip for controlling an audio power amplifier therein, and an audio signal processing method thereof.
2. Description of the Prior Art
Audio power amplifiers are circuits commonly used in modern electronic devices. Volume control of the audio power amplifier embraces: dynamically switching the audio power amplifier between a mute mode and an unmute mode according to user commands; and, when the audio power amplifier operates under the unmute mode, executing a volume control operation to adjust the output magnitude of the audio power amplifier according to the requirements of the user.
The volume control of the audio power amplifiers can be realized via selectively adopting different control interfaces each corresponding to different specifications. For instance, digital control interfaces complying with Serial Peripheral Interface (SPI) specification, Inter Integrated Circuit (I2C) specification, or Audio Codec 97 (AC' 97) specification can be used as the interface between a host and a slave including the audio power amplifier for transmitting the control signal to the control circuit via the applied digital control interface to control the operations of the audio power amplifier accordingly. However, the usable digital control interfaces for the aforementioned volume control require more than two connecting ports to connect the host with the audio amplifier circuit having the audio power amplifier; in addition, for the audio power amplifier, complicated signal transformation required for transmitting control signals to the audio amplifier circuit correctly according to the specification with which the control interface complies is unduly bulky and complex.
Another volume control method for the audio power amplifier controls the volume via analog signals at a DC level. Please refer to FIG. 1; FIG. 1 is a block diagram illustrating a conventional audio power amplifying circuit 100. As shown in FIG. 1, the audio power amplifier 130 receives audio signals from an input signal port 106; wherein a control circuit—e.g., a Micro-Controller Unit (MCU)—inside the host 190 generates an analog signal at a DC level and transmits the generated analog signal to the audio power amplifying circuit 100 via a first connecting port of the host 190 and a first connecting port 102 of the audio power amplifying circuit 100.
For volume control of the conventional audio power amplifying circuit 100, the audio power amplifying circuit 100 further needs to be equipped with an analog-to-digital converter (ADC) 110 for converting the received analog signal (from the first connecting port 102) into a digital signal; a gain control circuit 120 then receives the digital signal to thereby adjust a gain value of an audio power amplifier 130 for modulating the output volume. However, in addition to the aforementioned first connecting port 102 and the input signal port 106, the conventional audio power amplifying circuit 100 further requires an extra port for receiving the switching signal which selectively switches the audio power amplifier 130 between the mute mode and the unmute mode. For example, when there is no demand for hearing the audio output signal, the audio power amplifier 130 will go into the mute mode according to a control signal from the host 190; that is, an additional mute control signal generated by the host 190 is required wherein the host 190 transmits the mute control signal to the audio power amplifying circuit 100 via a second connecting port 192 of the host 190 and a second connecting port 104 of the audio power amplifying circuit 100. For the audio power amplifying circuit 100, the received mute control signal controls a switch 140 to be connected or disconnected; when the mute control signal controls the switch 140 to be connected, the audio signal received via the input signal port 106 will successfully be input into the audio power amplifier 130 to thereby amplify the audio signal according to the current gain value to output an audio output signal for driving a broadcasting device (e.g., a horn or a earphone); when the mute control signal controls the switch 140 to be disconnected, the audio signal received via the input signal port 108 will not be input to the audio power amplifier 130 and thereby the audio power amplifier 130 does not perform an amplifying operation and outputs no signals for maintaining the mute mode. In short, the audio power amplifier 130 selectively switches between the mute mode and the unmute mode according to the user commands via the connection or disconnection of the switch 140.
In addition, another existing volume control method is a mechanical method which generates an analog signal at the DC level via a variable resistance, which is then used to adjust a gain value of the audio power amplifier 130; however, the ADC is still required for converting the analog signal into a digital signal, which is transmitted to the audio power amplifier 130 for controlling the volume of the output audio.
The ADC 110 is an analog circuit where, under different manufacturing processes, the corresponding ADC 110 for the audio power amplifying circuit 100 differs; furthermore, the testing for the ADC 110 is excessively complex which increases the inconvenience of the overall design. In other words, circuit designs combining analog circuits with digital circuits lead to disadvantages both of design and manufacturing.
For conventional circuits, the audio power amplifying circuit usually requires at least two extra connecting ports (e.g., the first connecting port 102 and the second connecting port 104) other than the input signal port 106 which receives the input audio; the extra connecting ports are used, respectively, wherein one of the connecting ports receives the control signal to control the gain value of the audio power amplifier 130, and the other connecting port receives the mute control signal for switching the audio power amplifier 130 between the mute mode and the unmute mode.
Therefore providing a novel volume control method and corresponding circuit is necessary.